WELL; Really? The Claim: Never brush your teeth immediately after a meal

By ANAHAD O'CONNOR

Published: May 22, 2012

THE FACTS

Is there ever a bad time to brush your teeth?

Most of us believe that proper dental care means flossing and brushing often - at a minimum, twice daily, as the American Dental Association recommends. Those who are particularly diligent may brush more often, after meals, snacks or sugary drinks.

But research shows that brushing too soon after meals and drinks, especially those that are acidic, can do more harm than good. Acid reflux poses a similar problem: While it might seem like a good idea to brush after a reflux episode, doing so can damage your teeth.

Acid attacks the teeth, eroding enamel and the layer below it, called dentin. Brushing can accelerate this process, said Dr. Howard R. Gamble, president of the Academy of General Dentistry. ''With brushing, you could actually push the acid deeper into the enamel and the dentin,'' he said.

In one study, a group of volunteers were followed for three weeks as researchers examined the impact of brushing on their teeth after they drank diet soda. The scientists found an increase in dentin loss when brushing in the 20 minutes after drinking soda. But there was considerably less wear when brushing took place 30 or 60 minutes afterward.

''It is concluded that for protection of dentin surfaces,'' the authors wrote, ''at least 30 minutes should elapse before tooth brushing after an erosive attack.''

In the meantime, to get rid of acid, Dr. Gamble suggested rinsing the mouth out with water or using an acid-neutralizing mixture: one part baking soda, eight parts water.

THE BOTTOM LINE

Never brush immediately after an acidic meal or drink. Always wait at least 30 minutes.

scitimes@nytimes.comnThis is a more complete version of the story than the one that appeared in print.